The present invention relates to a hydraulic operating apparatus for a switch for switching (interrupting and closing) a circuit breaker.
Generally, in a switch such as a gas-insulated switch comprising a circuit breaker, an operator for driving a movable contact element constituting the circuit breaker is provided. The main components of the operator are: a hydraulic operating apparatus which comprises a pressure accumulator using a compressed gas such as N2 and in which a hydraulic fluid pressurized by the pressure accumulator acts on a piston to perform a switching operation: a pneumatic operating apparatus in which compressed air compressed in a pressure vessel by a compressor acts on a piston to perform a switching operation; and a spring operating apparatus in which a recoil force of a coil spring or belleville spring in an energy accumulating state acts to perform a switching operation. Among these operating apparatuses, the hydraulic operating apparatus is superior to the other operating apparatuses in view of its high-speed operation, small size, low noise, high output and the like but has such demerits as high cost, fluid leakage, and a large number of accessories. In the hydraulic operating apparatus, particularly, the pressure accumulator constituting a drive source has a structure in which the compressed gas acts on one surface of a pressure accumulation piston provided with a piston seal to thereby compress the hydraulic fluid, and, therefore, has a seal structure in which the hydraulic fluid and the compressed gas at an equal pressure are sealed gas-tight by a single seal at the piston seal portion. Due to the use of the compressed gas, this kind of pressure accumulator has the problem that the gas is contracted and expanded attendant on variations in the ambient temperature, with the result of variations in the pressure of the hydraulic fluid also. In contrast to this, there has been known a hydraulic operating apparatus in which a belleville spring is used in place of the pressure accumulation piston provided with the piston seal in the pressure accumulator so as to obviate the problem of variations in the pressure of the hydraulic fluid due to the variations in the ambient temperature (see, for example, Japanese Patent Laid-open Nos. 5-298968, 7-37801, 9-92097).
However, when the pressure accumulator in each of the conventional hydraulic operating apparatuses for switch performs high-speed successive operations (O—0.3 sec—CO—1 min—CO, CO—15 sec—CO, or the like) which are the required operations of the circuit breaker, the high-pressure hydraulic fluid in the pressure accumulator is consumed according to the operation and, simultaneously, the belleville spring having been compressed gradually releases the accumulated energy. Therefore, a difference in accumulated pressure is generated in the high-pressure hydraulic fluid between the first interrupting (cutoff) operation and the second interrupting operation, resulting in dispersion of the interrupting performance. In order to avoid this problem, it may be contemplated to enlarge the pressure accumulator in size so as to restrain the pressure variation of the high-pressure hydraulic fluid due to the successive interrupting operations, but this approach would enlarge the hydraulic operating apparatus for switch. For the hydraulic operating apparatus for switch, generally, a normal-time pressure variation range, a high-speed re-closing (O-0.3 sec- CO-1 min- CO) operation lock pressure, a closing (turning-ON) operation lock pressure, and an interrupting operation lock pressure are specified, based on the rated pressure. This makes it necessary to ensure the circuit interrupting performance of the apparatus for each of the operation lock pressures. In addition, the mechanical strength of the apparatus must be designed for the maximum value in the normal-time pressure range. As a result, there is a difference of not less than 130% between the minimum pressure for ensuring the circuit interrupting performance and the maximum pressure for ensuring the mechanical performance. Accordingly, a very uneconomical designing has been required.